Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$117.72	13.226%	$133.2896	$133.29	$133.30	$133.30
Purchase #2	$162.77	10.190%	$179.3563	$179.36	$179.35	$179.40
Purchase #3	$28.62	13.271%	$32.4182	$32.42	$32.40	$32.40
Purchase #4	$66.49	9.149%	$72.5732	$72.57	$72.55	$72.60
Purchase #5	$86.26	3.653%	$89.4111	$89.41	$89.40	$89.40
Purchase #6	$47.91	4.197%	$49.9208	$49.92	$49.90	$49.90
Purchase #7	$28.63	10.433%	$31.617	$31.62	$31.60	$31.60
7 purchase totals =	$538.40		$588.5862	$588.59	$588.50	$588.60